From mboxrd@z Thu Jan  1 00:00:00 1970
From: Thomas Chou <thomas@wytron.com.tw>
Date: Sun, 27 Dec 2015 16:21:54 +0800
Subject: [U-Boot] [PATCH v4 4/8] mips: ath79: add serial driver for
 ar933x SOC
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References: <1451069788-6786-1-git-send-email-wills.wang@live.com>
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 <567E941C.9090300@gmail.com> <BLU437-SMTP303510F525B3851CF0612CFFFA0@phx.gbl>
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To: u-boot@lists.denx.de

Hi Wills,

On 2015?12?27? 14:28, Wills Wang wrote:
>>> +static int ar933x_serial_putc(struct udevice *dev, const char c)
>>> +{
>>> +    u32 data;
>>> +
>>> +    if (c == '\n')
>>> +        ar933x_serial_putc(dev, '\r');
>> remove this, the serial core driver takes care of it
>>
>>> +
>>> +    do {
>>> +        data = ar933x_serial_read(dev, AR933X_UART_DATA_REG);
>>> +    } while (!(data & AR933X_UART_DATA_TX_CSR));
>> remove this, the serial core driver takes care of it via your pending
>> callback (ar933x_serial_pending)
>>
>
> Serial core driver don't query and wait the pending function before
> "serial_getc" and "serial_putc", so these statements can't remove,
> or board don't work.

As I wrote in the v3 patch review, both the getc() and putc() should 
return -EAGAIN if there is no available data to read or not ready to 
write. The polling is done in the serial-uclass.c

Regards,
Thomas